I would like to play around with Xen with the intention of eventually running a bunch of different services on separate virtual machines (partly just because I can), and have the possibility of trying things like clusters and such. I've decided to use Xen over KVM (simply because KVM doesn't seem as feature-complete just yet, I think I'll try it sometime next year) and over VMWare Server ESXi (primarily because Xen looks more interesting, and also has more features).
Now, looking at the distros that can be used as a dom0, I've narrowed it down to 2 choices: CentOS 5 and OpenSolaris.
CentOS has an advantage in the setup seems like it would be much simpler (and looks better documented), and I have experience with Fedora, which should (hopefully) transition over.
On the other hand, OpenSolaris has ZFS and Project Crossbow, both of which are appealing to me. (ZFS for the advantages over ext(3|4), Project Crossbow for the interesting virtual network features, which may be something useful with all the VMs.) However, I have no experience whatsoever with OpenSolaris, so there would be a steeper learning curve, but I'm willing to learn.
At this point, I'm leaning towards running CentOS as the dom0, with OpenSolaris as one of the domUs. (I can always re-build the system with OpenSolaris as the dom0 anyway, I guess.)
Have I overlooked any gotchas, or is my reasoning sound?
Clarification: Specifically, what I'm looking for are any particular (dis)advantages of using one OS for the dom0 over the other.
For example, restating the above, CentOS has the advantages of: + being related to a system I know (Fedora vs Solaris) + Good documentation with regards to installing Xen
While OpenSolaris has: + ZFS, which seems to be an excellent improvement over what ext3 or ext4 offer (I'm not going to use btrfs yet.) + Project Crossbow, which may or may not be useful when it comes to setting up the network interfaces that each VM will use.
(Thanks to TrueDuality for adding the 'dom0' tag. Apparently as a new user, I can't create new tags.)